1. Field of the Invention
This invention relates to an improved geophone case for use in wetland areas.
2. Discussion of the Prior Art
In wetland areas, marshes and the like, geophones as used in seismic exploration are enclosed in special cases or housings. A marsh case is generally long and slender; one end, the lower end, of the case is pointed to facilitate insertion of the unit into mud. The other, upper end of the case has a cable entry port through which an electric cable is sealed. The cable conducts the geophone signals to the outside world. The upper end of the case is designed to fit a tool on the end of a long pole so that the marsh geophone can be shoved into the mud. The cable entry port must, of course, be sealed against entry of moisture.
When geophysical operations are completed at a given location, the geophone is recovered from the mud by pulling it out by the cable. The cable must therefore be firmly anchored internally of the case. For example, see U.S. Pat. No. 3,931,453, assigned by mesne assignments to a sister firm of the assignee of this invention.
Although the cable itself is firmly anchored interiorly of the case, when a pull is applied, the cable necessarily stretches. Because it is stretched, the diameter of the cable tends to diminish; it tends to "neck out", particularly at the cable entry port of the case. During use, the constant stretching and relaxation of the cable with respect to the water seal assembly creates undesired leakage problems. Moisture penetrates the seal into the geophone chamber causing corrosion and electrical problems.